The invention relates to a method for depositing a flattened droplet on a surface suitable for in vitro fertilization (IVF) and embryo transfer (ET), and apparatus therefore, and a pump therefor.
In an IVF-ET procedure, oocytes are aspirated from female ovaries and inseminated in vitro with male sperm in a culture medium to form embryos which are incubated prior to their being transferred to a subject by means of a two-stage transfer procedure. The transfer procedure includes the aspiration of a relatively large volume of about 20-40 xcexcl of culture medium containing between one to five embryos into a transfer catheter by means of a manually operated syringe and its subsequent injection into a subject.
Since a conventional IVF-ET procedure is manual, the rate of injection of the embryo containing culture into a uterine cavity may vary significantly. Thus, on the one hand, too slow an injection rate may cause embryo containing culture medium to trickle down the transfer catheter""s outer surface and, on the other hand, too quick an injection rate may severely damage embryo(s) following their collision against a uterine wall. The latter case may also flood a subject""s uterus possibly resulting in a failed procedure as embryos are either washed out of her uterus or implanted in one of her Fallopian tubes leading to an ectopic pregnancy. Another disadvantage attendant with the use of a relatively large volume of culture medium is that it may alter the specific properties of the micro-environment within a subject""s uterus required for successful embryo implantation and its normal development.
The present invention is based on the notion that substantially automating embryo implantation in IVF-ET procedures may overcome some of the shortcomings of the conventional IVF-ET procedure.
In accordance with the present invention, there is provided a method for depositing a flattened droplet on a surface particularly suitable for depositing embryo(s) containing culture medium at a desired site in a uterus cavity, and apparatus therefor, and a pump therefor.
In accordance with a first aspect of the invention, there is provided a method for depositing a flattened droplet on a partially absorbent surface, the method comprising the steps of:
(a) providing a narrow bore transfer tube having a proximal end and a distal end and containing a microvolume of liquid, the proximal end connected to a pneumatic system for issuing an outgoing flow of displacement gas into the transfer tube and drawing an incoming flow of displacement gas thereinto from the transfer tube; and
(b) issuing an outgoing flow of displacement gas for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface-and controllably blowing one or more bubbles into the droplet towards the end of its discharge to flatten the droplet on the surface.
A xe2x80x9cflattened dropletxe2x80x9d in the context of the present invention can be demonstrated on standard 80 gram/m2 A4 paper for use with ink jet printers, such paper constituting a partially absorbent surface on which a flattened droplet of the present invention has a projected surface area about three to six times larger than that of a naturally forming dome-like droplet. A xe2x80x9cpartially absorbent surfacexe2x80x9d in the context of the present invention is one which absorbs a relatively insignificant volume of a naturally forming dome-like droplet over about 60 seconds. The flattening of a droplet as achieved by the method of the present invention is not by the relatively slow process of its being absorbed assuming it does not dry but rather as a consequence of its being effectively inflated by one or more bubbles of displacement gas controllably blown thereinto towards the end of its discharge which typically occurs over 5-20 seconds from an initial outward displacement of the microvolume of liquid. The surface may be flat, inclined or even inverted and still maintain the droplet in its flattened shape by virtue of the prevailing surface tension therewith.
A xe2x80x9cmicrovolume of liquidxe2x80x9d in the context of the present invention is a volume of liquid in the microliter range, e.g., within the range of 0.05-5 xcexcl, preferably within the range of 0.1-3.0 xcexcl, and particularly within the range of 0.3-2.0 xcexcl. In the case of an IVF-ET procedure on a human subject when the catheter is upwardly inclined, even though the discharge of culture medium is relatively slow, its volume is so small so as to avoid a downward trickle along the catheter""s outer surface.
In accordance with a preferred embodiment of the present invention, step (a) includes:
(a1) preventing capillary forces to draw liquid into the transfer tube upon insertion of its distal end into a vessel containing liquid;
(a2) inserting the transfer tube""s distal end into the liquid;
(a3) drawing an incoming flow of displacement gas from the transfer tube such that a microvolume of liquid is drawn thereinto; and
(a4) removing the transfer tube""s distal end from the liquid.
The step of preventing capillary forces is preferably achieved by issuing an outgoing flow of displacement gas into the transfer tube so as to create a positive pressure therein. Alternatively, this step can be achieved, for example, by providing a seal at its distal end. After the transfer tube""s distal end is removed from the liquid, the microvolume of liquid is preferably inwardly drawn away from its distal end as a safety precaution whereafter the inward displacement is neutralized by a brief outgoing flow of displacement gas into the transfer tube.
After the discharge of the microvolume of liquid from the transfer tube, the flattened droplet in most cases is still connected to the transfer tube""s distal end and therefore to prevent its suction back into the transfer tube, the outgoing flow of displacement gas is maintained until the droplet is disconnected from the transfer tube""s distal end by manually withdrawing the transfer tube. This outgoing flow of displacement gas may also remove any small quantities of the microvolume which were not initially discharged and which may include an embryo(s) in an IVF-ET procedure.
In accordance with a second aspect of the present invention, there is provided apparatus for depositing a flattened droplet of liquid on a partially absorbent surface, the apparatus for use with a narrow bore transfer tube having a proximal end and a distal end and a vessel of liquid, the apparatus comprising:
(a) a pneumatic system connected to the transfer tube""s proximal end and adapted for issuing an outgoing flow of displacement gas into said transfer tube and drawing an incoming flow of displacement gas thereinto from said transfer tube; and
(b) a control mechanism for controlling said pneumatic system in different operational modes including:
a user controlled suction mode for drawing an incoming flow of displacement gas from the transfer tube whereby a microvolume of liquid is drawn thereinto prior to the removal of said distal end from the vessel; and
a user initiated automated delivery mode for issuing an outgoing flow of displacement gas into the transfer tube for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface and controllably blowing one or more bubbles into the droplet towards the end of its discharge to flatten the droplet on the surface.
In accordance with a third aspect of the present invention, there is provided a pump comprising a housing having a bore with an internal peripheral surface, and a stationary annular sealing member integrally formed therewith at a first end of a pair of opposite ends; a slide rod disposed in said bore and having an external peripheral surface and a displacement annular sealing member integrally formed therewith; said sealing members sealing said peripheral surfaces to define a vented displacement volume therebetween whose volume is proportional to an annular cross section area between said peripheral surfaces and a distance between said sealing members; and said slide rod being slidably reciprocable between first and second positions respectively toward and away from said stationary sealing member whereupon said displaceable sealing member moves to reduce said volume to issue an outgoing flow of displacement gas from said displacement volume on a downstroke of said slide rod from said second position to said first position and said displaceable sealing member moves to increase said volume to draw an incoming flow of displacement gas into said displacement volume on an upstroke of said slide rod from said first position to said second position.
Preferably both the bore and the slide rod are of a right cylindrical shape such that the displacement volume has a cross sectional area defined by xcfx80(a2-a2) where a and b are the radii of the bore""s internal peripheral surface and the slide rod""s external peripheral surface, respectively. Preferably, the cross section area is in the order of 4-10 mm2 and the pump has a displacement volume incrementally changeable in the order of 0.1-0.4 xcexcl.